Elastomeric surfaces of articles, in general, exhibit poor lubricity with respect to a dry surface, such as dry skin or other mammalian tissue. These properties are due to surface friction. Additionally, many elastomeric articles or surfaces display poor lubricity with respect to damp surfaces.
A high surface friction coefficient is useful for many applications such as tire treads, flooring and footwear. However, these same properties are a distinct disadvantage in many other applications and especially in those applications wherein an elastomeric surface must slide on another surface, such as in the donning of gloves over dry or damp skin. This is particularly important in the use of medical gloves, such as examination gloves and surgeon's gloves. These gloves are relatively close- fitting in order to provide sensitivity. Furthermore, most surgeons don their gloves after scrubbing up and without having fully dried their hands, so that areas of their hands may be dry while other areas may be distinctly damp. Consequently, the elastomeric materials useful in such applications must exhibit concurrently enhanced lubricity with respect to dry surfaces (dry slip), enhanced lubricity with respect to damp surfaces (damp slip), as well as the requisite mechanical properties (flexibility, strength, etc.).
Conventionally, dry slip is achieved by the use of powder lubricants such as magnesium carbonate, starch and talc. However, if the hands are damp, the use of a powder is counter-productive and may actually inhibit donning. Furthermore, in surgery, there is a risk of loose powder contaminating the surgical field. These materials can also cause irritation and may be allergenic.
Chlorination of rubber has also been proposed for the purpose of reducing tackiness and decreasing the coefficient of friction of rubber. (See Romberg, "Aqueous Chlorination of Natural Rubber Surfaces", A.C.S. Rubber Division, Spring Meeting (1986); T.C.Q. Noakes, Proc. Int. Rubb. Technol. Conf., Penang, Malaysia (1988); Natural Rubber Technical Information Sheet No. 17, The Malaysian Rubber Producers' Research Association, Latex Series (1977); D.C. Blackley, "High Polymer Lattices", Palmerton Publishing Company (1966), p. 548, and PCT/GB92/00171, published as WO 92 13497. However, chlorination can adversely affect the mechanical properties of flexible elastomeric articles such as rubber gloves and is better avoided for this reason. In addition, chlorination produces surfaces which have very poor damp slip.
Polymeric lubricant coatings which are bonded to the tissue-contacting glove surface or are embedded in the rubber itself have been proposed for the purpose of reducing surface friction of rubber in, for example, U.S. Pat. Nos. 3,813,695; 3,856,561; 4,070,713; 4,143,109; and 4,302,852. U.S. Pat. No. 3,813,695, in particular, describes a laminated surgical glove having a flexible outer layer and a hydrophilic plastic (hydrogel polymer) inner layer. Other articles such as catheters and bathing caps coated with hydrophilic polymers are described in U.S. Pat. Nos. 3,326,742; 3,585,103; 3,607,433; 3,745,042; 3,901,755; 3,925,138; 3,930,076; 3,940,533; 3,966,530; 4,024,317; 4,110,495; and 4,125,477 as well as British Patent Publication Nos. 1028446 and 859297.
James et al., U.S. Pat. Nos. 4,499,154 and 4,575,476, describe treating a rubber article having a coating of a lubricated hydrogel polymer (inherently providing dry slip) bonded layer, with a surfactant material, such as a quaternary ammonium cationic surfactant, or a long chain fatty amine material to improve the lubricity of the coating with respect to damp skin.
U.S. Pat. Nos. 4,143,109 and 4,070,713, and British Patent 1,541,155, propose the use on the skin-contacting surface of an elastomeric medical glove of a second layer of elastomeric material bearing partially-embedded particulate matter (cross-linked starch particles or polyethylene, or ethylene-vinyl acetate copolymer particles 5-40 microns in size). The elastomeric material forming the second layer is said to adhere to both the particles and the elastomeric glove substrate. Carboxylated styrene-butadiene latex, brominated butyl rubber and styrene-polyethylene/butylene-styrene block copolymer are disclosed as specific elastomeric materials suitable for use in forming the particle-bearing layer. The patents state that (i) the elastomeric substrate can be 125-175 microns thick; (ii) the inner layer can be 5-30 microns thick; and (iii) the particle size should be greater than the thickness of the second layer. In all the examples, however, the layer is 15 microns thick, i.e. 10% of the thickness of the laminated glove and 37.5-300% of the thickness of the particles. The resulting gloves are said to be donned easily without the use of additional lubricants, such as dusting powder. The particles described all appear to be organic, solid, essentially nonporous particles. Moreover, as far as the present inventors know, the gloves described in these patents have never been commercialized despite a felt need in the art for powder-free gloves.
European Patent Application EP 543,657 published May 26, 1993 discloses powder-free elastomeric medical gloves comprising a layer of an antiblocking composition (serving as a binder) with particles distributed throughout. The majority of the particles must have a size greater than the thickness of the antiblocking composition in the layer. The antiblocking composition should have mechanical properties comparable to those of the elastomer substrate. Polyurethane aqueous dispersion is said to be preferred as the binder. The particles can be cross-linked corn starch, nylon, polyurethane or mixtures and should be of a size range between 5 and 50 .mu.m with an average size between 30 and 40 .mu.m. This EP application does not disclose nor suggest the requirement that specific properties of the particles or the binder be present or have values within specified ranges that would result in good dry and wet slip as well as good adhesion to the substrate.
It has now been discovered that the dry slip and the damp slip properties of elastomeric articles can be improved substantially by providing on the wearer-contacting surface of these articles a thin layer of an adhering binder material bearing porous, absorbent microparticles and subsequently applying a surfactant or a long chain fatty amine. Under a scanning electron microscope the microparticles appear to be coated by the binder even though they are partially protruding therefrom to give a microroughened (globular reticulated) appearance to the coating, as depicted for example in FIG. 1.